My iOS solution is uninstalling YouTube so the links will open in a default browser instead, setting the default to Firefox Focus, and installing PocketTube, where you have to be logged into YT so it downloads your subscriptions and latest videos. Use it to organize your subscriptions into group playlists, then hit a button in the corner while viewing a list for it to forward the list to FF Focus. The only gripe I have about it is that every time a new video from the playlist loads, you have to toggle fullscreen on again because it’s effectively opening a new page in FF Focus. You can also watch videos directly in PocketTube by tapping an individual video, and also seems to skip ads, but you don’t have subtitles that way.
Afaik this works by itself, but I also have the $1.99 Vinegar extension for Safari installed which may or not contribute to the ad blocking. I’d try it without first to see what happens.
edit: This is also my solution on Android, except I have PocketTube open the list in YT Revanced, where optionally I can cast the list to SmartTube on my FireTV including SponsorBlocks. The only place I’m logged in is PocketTube.
NotTheOnlyGamer